1. Field of the Invention
The present invention pertains to a patch-excited non-inclined radiating slot waveguide, of the type having slots perpendicular to the axis of the guide, cut out on a narrow wall of the guide with a spacing substantially equal to a half wavelength of operation in the guide.
2. Description of the Prior Art
Slot waveguides are frequently used as linear arrays of radiating sources in antenna arrays, for example in radar. They have the advantages of low cost and low losses. T obtain radiation close to the perpendicular to the waveguide, and good matching, there should be, firstly, a distance between successive slots that is close to .lambda.g/2, where .lambda.g is the wavelength in the waveguide and, secondly, a supplementary phase shift of .pi. between two consecutive slots.
These conditions can be met with slots positioned in the broad wall of a rectangular-section waveguide or on the narrow wall. The fact that the slots are positioned in the broad wall has many drawbacks, notably a big pitch between successive waveguides. This restricts the scanning angle of the beam in a plane perpendicular to the waveguides. It is preferred, therefore, to use slots on the narrow wall of the waveguides.
If the slots are perpendicular to the axis of the waveguide, there is no energy coupling between the slots and the waveguide, and the radiation is zero.
In a first approach to this problem, therefore, the slots are inclined alternately on either side to obtain the above-stated necessary conditions. However, owing to the inclination of the slots, this approach has the drawback of radiating a cross-polarized component which ma attain levels incompatible with the efficient operation of the antenna using these waveguides.
Another known approach, then, consists in using slots that are not inclined (i.e. that are perpendicular to the axis of the waveguide) and in exciting them by means of an obstacle (for example, irises or rods) placed in the waveguide.
In particular, the U.S. Pat. No. 4,435,715 (Hughes Aircraft) describes a waveguide with non-inclined slots in which the excitation of a slot is obtained by placing conductive rods on either side of the slot. Each slot is positioned between an edge of the slot and one of the broad walls of the waveguide. However, an approach such as this has the drawback of being costly to implement. Indeed, the rods have to be fixed individually within the waveguide, for example by dip soldering.